Complementary metal oxide semiconductor (CMOS) image sensors (hereinafter referred to as CIS) are used as image pickup elements in, for example, digital still cameras and digital video cameras. With the increase in the number of pixels and reduction in optical size of the CIS, the pixel size has been reduced and the pixel density has been increased.
As a result of the reduction in pixel size and increase in pixel density, sensitivity per unit pixel has been reduced and there is a possibility that a signal-to-noise (S/N) ratio will be reduced and image quality will be degraded. In addition, since the distance between the adjacent pixels has been reduced, there is a possibility that pixels expected to receive only light in a specific wavelength range (for example, green light) will receive light in other wavelength ranges (for example, red or blue light) and color mixing will occur, which leads to a reduction in color reproducibility.
To solve the above-described problems, a back-illuminated CIS in which a grid-shaped light-shielding material is arranged so as to extend between the adjacent pixels has been proposed. In this back-illuminated CIS, light is incident on a back surface at the side opposite to a front surface on which a wiring layer is formed, and the incident light reaches a photodiode (PD) region of a silicon (Si) substrate without being blocked by the wiring layer. Therefore, the reduction in sensitivity per unit pixel can be suppressed.
In addition, obliquely incident light is reflected by the grid-shaped light-shielding material arranged so as to extend between the adjacent pixels, and is suppressed from being incident on pixels other than the pixels on which the light is expected to be incident. As a result, color mixing can be reduced and reduction in color reproducibility can be suppressed.